(1) Field of the Invention
The present invention relates to a compressor for an air-conditioning system used in a vehicle such as an automobile, more particularly, to a multi-piston swash plate type compressor fitted with an internal sealing device and able to ensure a uniform distribution of refrigerant to cylinder bores.
(2) Description of the Related Art
A multi-piston swash plate type compressor for use in a vehicle air-conditioning system is well known, as disclosed in, for example, U.S. Pat. Nos. 4,070,136, 4,403,921, and 4,717,313 to the same assignee as of the present application. In general, such a multi-piston swash plate type compressor comprises: front and rear cylinder blocks axially combined together to form a swash plate chamber therebetween, the combined cylinder blocks having a same number of cylinder bores radially formed therein and arranged with respect to the central axis thereof, the cylinder bores of the front cylinder block being aligned and registrated with the cylinder bores of the rear cylinder block, respectively, with the swash plate chamber intervening therebetween; double-headed pistons slidably received in the pairs of aligned cylinder bores, respectively; front and rear housings connected to the front and rear end faces of the combined cylinder blocks through the intermediary of front and rear valve plates, respectively, the front and rear housings each forming a suction chamber and a discharge chamber together with the corresponding one of the front and rear valve plates; a rotatable drive shaft axially extended through the front housing and the combined cylinder blocks; and a swash plate securely mounted on the drive shaft within the swash plate chamber, and engaging with the double-headed pistons to cause these pistons to be reciprocated in the pairs of aligned cylinder bores, respectively, by rotation of the swash plate. The front and rear cylinder blocks, the front and rear valve plates and the front and rear housings are axially and tightly assembled as an integrated unit by a plurality of long screw bolts.
Referring to the front and rear valve plates in particular, which may have substantially the same construction, each plate comprises: a disc-like member provided with sets of a suction port and a discharge port, each set of which is able to communicate with the corresponding one of the cylinder bores of the front or rear cylinder block; a first valve sheet member attached to the inner side surface of the disc-like member and opposed to the corresponding end face of the combined cylinder blocks, and having suction reed valve elements formed therein, each of which valve elements is arranged so as to open and close the corresponding suction port of the disc-like member; and a second valve sheet member attached to the outer side surface of the disc-like member and having discharge reed valve elements formed therein, each of which valve elements is arranged so as to open and close the corresponding discharge port of the disc-like member. Each of the front and rear valve plates is also provided with suction openings which are aligned with passageways formed in the front or rear cylinder block, respectively, whereby the suction chambers formed in the front and rear cylinder blocks are communicated with the swash plate chamber into which a refrigerant is introduced from an evaporator of an air-conditioning system through a suitable inlet port formed in the combined cylinder blocks.
In the multi-piston swash plate type compressor as mentioned above, the drive shaft is driven by the engine of a vehicle such as an automobile so that the swash plate is rotated within the swash plate chamber. The rotational movement of the swash plate causes the double-headed pistons to be reciprocated in the pairs of aligned cylinder bores so that the pistons alternately execute a suction stroke and a compression stroke. When each of the pistons executes the suction stroke, the suction reed valve element is opened and the discharge reed valve element is closed, so that the refrigerant is sucked into the cylinder bore from the suction chamber, which is communicated with the swash plate chamber, through the suction port of the front or rear valve plate, and when the piston executes the compression stroke, the suction reed valve element is closed and the discharge reed valve element is opened, so that the sucked refrigerant is compressed and discharged into the discharge chamber through the discharge port of the front or rear valve plate.
As is well known, the refrigerant in the air-conditioning system includes a lubricating oil dispersed therein as a mist. This is to ensure that movable parts of the compressor, such as the double-headed pistons, the swash plate, thrust bearings of the swash plate, radial bearings of the drive shaft, etc., are lubricated with the lubricating oil included in the refrigerant during the passage of the refrigerant through the compressor.
The conventional compressor can be provided with either of two different arrangements of the suction and discharge chambers, i.e., the suction chamber is arranged inside the discharge chamber in the front and rear housings, or the suction chamber is arranged outside the discharge chamber in the front and rear housings. The former arrangement possesses an advantage of simplifying the internal construction of the front housing because a sealing portion of the drive shaft disposed adjacent to the suction chamber need not be isolated therefrom due to a low pressure created in the suction chamber. In the multi-piston swash plate type compressor employing the inside suction chamber arrangement, as disclosed in, for example, Japanese Examined Patent Publication No. 56-27710 and U.S. Pat. No. 4,717,313, the suction and discharge chamber are formed in inner and outer annular chambers which are separated from each other by an annular partition wall integrally projected from the inner side wall surfaces of the front and rear housings.
As stated above, the front and rear cylinder blocks, the front and rear valve plates, and the front and rear housings are axially and tightly assembled as an integrated unit by a plurality of long screw bolts. In this case, since the screw bolts are extended around the periphery of the integrated unit, the central portion of the front and rear valve plates, i.e., the portion facing the suction chamber of the front and rear housings, is less affected by a clamping force of the screw bolts than the peripheral portion of the valve plates. For this reason, the central portion of the front and rear valve plates may be forcibly deformed and separated from the corresponding end face of the combined cylinder blocks, because the front and rear valve plates are subjected to the high pressure of the compressed refrigerant, and as is obvious, when such deformation occurs, the sealing between the front and rear valve plates and the end faces of the combined cylinder blocks is usually broken. The annular partition wall separating the suction and discharge chambers also serves to suppress deformation of the front and rear valve plates. In particular, the annular partition wall is projected from the inner side wall surface of the front and rear housings in such a manner that the projected annular end face thereof abuts against the outer side surface of the front and rear valve plates when the unit is assembled, whereby deformation is suppressed by the annular partition wall abutting against the outer side surface of the front and rear valve plates.
Nevertheless, in a multi-piston swash plate type compressor, especially a ten-cylinder (five front and five rear) swash plate type compressor, it is very difficult to completely suppress deformation of the front and rear valve plates only by the annular partition wall, because a slight gap is formed through which the high pressure refrigerant compressed within the cylinder bores is easily and directly diverted into the passageways formed in the cylinder blocks, as pointed out in U.S. Pat. No. 4,717,313, which leads to a lowering of the compression efficiency of the compressor, and accordingly, the cooling efficiency of the air-conditioning system.
U.S. Pat. No. 4,717,313 is directed to a complete suppression of the deformation of the front and rear valve plates by using support ribs which are projected from the inner side wall surface of the front and rear housings so that the projected end faces thereof abut against the outer side surface of the front and rear valve plates, thereby preventing the formation of the slight gap mentioned above.
Nevertheless, U.S. Pat. No. 4,717,313 fails to eliminate another drawback inherently involved in the multi-piston swash plate type compressor. Namely, in particular, the refrigerant introduced into the swash plate chamber through the inlet port is influenced by the rotational movement of the swash plate and thus tends to circulate in the rotational direction of the swash plate. This circulating flow of refrigerant, which starts at the inlet port, is gradually reduced because a portion of the circulating refrigerant flow successively enters the passageways of the cylinder blocks and the respective flow rates of refrigerant passing through the passageways of the cylinder blocks then become different from each other. For this reason, the refrigerant entering into the suction chamber through the passageways has a very unbalanced density and cannot be uniformly delivered and distributed to the cylinder bores. As a result, a lack of lubricating oil occurs in a cylinder bore to which only a small amount of the refrigerant including the lubricating oil is delivered, whereby a seizure of the pistons therein may occur. Especially, the cylinder bores disposed adjacent to the passageways through which the refrigerant passes at a small flow rate are liable to lack lubrication. In the multi-piston swash plate type compressor as disclosed in U.S. Pat. No. 4,717,313, the lack of lubrication may be worsened due to the existence of the support ribs provided within the suction chamber.